Properly disable bluetooth when not needed/configured

[nis65]

I recently moved. So my multiroom setup changed heavily, i renamed multiple devices (including ones with a snapserver on it). At the old flat, all devices had a configured bluealsa-workaround-cable just because it was so easy to configure with these playbooks (and so cumbersome before without).

Now, I will probably only need bluetooth on 3 of the 6 devices. I manually deconfigured some of them, but I noticed later that they still show up on my mobile.

As discussed today, I will make a proposal how to properly disable bluetooth if desired:

• use rfkill?
• remove all unneeded software modules? The goal is to remove unneded radiation and power consumption. So stopping/disabling services is probably good enough.

[nis65]

Did some tests today: Streaming some audio over bluetooth to a node and then entered on the Raspi:

rfkill block bluetooth

Immediately, the bluetooth connection is stopped (also visible on the client). rfkill list shows Bluetooth as

1: hci0: Bluetooth
        Soft blocked: yes
        Hard blocked: no

This is expected, "Hard blocked" would mean that some hardware switch has disabled bluetooth (which is not available on the Raspi afaik).

Unblocking bluetooth later with

rfkill unblock bluetooth

makes the bluetooth connection available again immediately and I can reconnect (as before) and stream again.

[nis65]

So I think the nicest implementation would be as follows:

• explicitly unblock bluetooth for devices with an enabled bluetooth sink
• explicitly block bluetooth for devices without confgured bluetooth sink

While this does not uninstall anything that was installed before when then node was "with bluetooth", it still disables bluetooth properly. For pristine systems, it is a perfect implementation, for modified ones it is good enough.

[nis65]

fix merged in #47